Summary:
The DtpA protein (formerly TppB) is a member of the POT (proton-dependent oligopeptide transporter) family of peptide transporters [Paulsen94a] also known as the PTR (peptide transport) family. DtpA is responsible for proton-dependent transport of di- and tripeptides as well as some structurally related peptidomimetics like B-lactam antibiotics [Weitz07, Harder08]. DtpA transports the tetrapeptide, tetraalanine in vitro [Prabhala14] however tetraalanine does not function as an inhibitor in competitive transport assays [Weitz07]. DtpA shows a preference for di- and tripeptides composed of L amino acids and for peptides containing a positively charged side chain in the N-terminal position [Harder08].

Transmission electron microscopy of solubilised DtpA suggests a monomeric crown-like structure with a pore of approximately 8 nm [Weitz07]. DtpA is predicted to contain 14 transmembrane regions with both termini located in the cytoplasm [Bippes13]. Characterisation of DtpA embedded in a lipid membrane indicates that the protein adopts two alternate conformational states defined largely by the stabilisation of transmembrane helix 2 (TMH2). Binding of an inhibitor molecule shifts the equilibrium between these two states towards the conformation containing a stabilised TMH2 [Bippes13].

dtpA was identified as a member of the OmpR regulon in a DNA microarray experiment [Oshima02]. dtpA expression is transcriptionally regulated by OmpR, but is not sensitive to changes in medium osmolarity [Goh04].